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accumulation rate at present indicates that the
seal may have reseated itself.
Electrical System
T. L. Hudson
Power to the MSRE electrical system is supplied
from the OKNJL substation by either of two 13.8-
kv TVA power Isnes, a preferred line or an alter-
nate. During this report period, while operating
on the preferred feeder, there were two unscheduled
electrical interruptions when the reactor was at
power, During a thunderstorm on June 2.5, the
reactor operation was interrupted by the loss of
both feeders. Two amplifiers were damaged on the
reactor period safety system, Approximately 32
hr later, the reactor was returried to critical opera-
tion after the period safety amplifiers had been
repaired. On July 12, the other interruption was
caused by the loss of the preferred feeder during
another thiinder:;torm. Einergency power from the
diesel generators was in service within 2 min, and
low-power nuclear operation was resumed in
about 13 min. After repairs had been completed
on the preferred feeder, full-power operation was
resumed in approximately 5 hr.
Difficulty was experienced in run 12 when re-
starting main blower 1. The breaker tripped off
the blower during the starting sequence for several
attempted starts. On a later occasion, the breaker
tripped several limes before main blower 1 was
started. This erratic behavior was explained when
a loose gasket was found in one of :he time-
delay orifj.ces when the breaker was checked in
August, Tests have been made that indicate the
total time of the starting sequence is too long
when compared with maximum time delay of the
breaker overload element. Therefore, the total
t.ime of the start sequence will be reduced from
25 to 12 sec.
Heaters
T. L. Hudson
The last of six heating elements in heater HX-I
failed on October 28, 1966. Satisfactory heat cx-
changer temperatures were maintained without this
heater, even with the fuel loop empty. However,
continuous circulation of the coolant salt was
rnclintained until after run 11, so the full effect of
the heater failurc could not be detetmined. Tests
3 1.
were performed with both the fuel and coolant
loops empty after run 11 to determine the need for
this heater in preheating the system from a cold
condition. When helium circulation was stopped
in the fuel system, the temperature distribution
was satisfactory for a fill without heater IIX-1
operating. However, with helium circulation in
the fuel system, “cold” helium was introduced
possibly from the fuel pump -- and one temperature
decreased to below 800°F. Since satisfactory
tempera.tures could be achieved without it, the
failed heater w i not ~ ~ replaced.
Radiator heater CK6-413 failed on March 30, 1967,
and was replaced with a spare heater (CRI-3C).
During the shutdown after run 11 f.he electrical
lead to heater CR5-IB was repaired, and the heater
was placed back in service. Several broken
ceramic bushings were also replaced at this time.
Control Rods and Drives
M. Richardson
Performance of the control rods and drives has
been within the operating limits this period. No
mechanical failures of the rods or drives have
occurred. The fine-position synchro of rod 2,
which had failed during the previous period, was
replaced prior to the beginning of run 12. The
drive unit for this rod was inspected at the same
time and found to be in excellent condition. The
grease in the drive unit appeared unchanged after
a total radiation dose of about 10’ rads and there-
fore was not replaced.
After run 12, routine checks of absolute rod
position using the single-point indicators in the
rod thimbles revealed an apparent upward shift
of 0,s in. for rod 1. Since there was an equivalent
shifi in the upper and lower limit switches, it is
believed that this shift was caused by slippage
of the drive chain on one of the sprockets after a
rod scram. The exact time of the shift is not
known because, between the absolute positron
measurements, there were control rod scrams be-
fore and after run 12.
Salt Samplers
K. B. Gallaher
Fuel Sampler-Enricher. -- The fuel sampler-
enricher wcls used intensively during this report
period with only a few minor difficulties until the